EXERCISE 1A good three-dimensional result, Claire. I'm happier with your bricks than I am with the mortar, so I'll tackle them separately.

Ideally, you should have found different techniques for the mortar and bricks to reinforce the fact that they have completely different textures.

The bricks have three-dimensional features but, as far as I can see, most appear to be flat marks on the surface. Some do have an internal top shadow but depressions work better visually if you apply a little exaggeration. If you give each depression a thin shadow at the top and a thin highlight at the bottom, you will provide the necessary visual clues. There is only one situation when that shadow and highlight combination are present, and that's a depression. [see image below]

Leaving white within the mortar was a good idea, because the extra contrast obtained is one of the things that makes it look different from the bricks. But that's almost all the difference here. The mortar lacks texture and this exercise gave the opportunity to apply three-dimensional modelling to the mortar, and in such a way that it was unmistakably not brick. This is old lime mortar but even modern cement mortar has a sandy and grainy texture.

I'm not expecting you to be fully conversant with mortar, but you just need to describe it to yourself before you begin. In this case, it's grainy, it is rough with sharp edges, it's weathered so it has pieces missing and deep holes and fissures. Once you have that in mind, the drawing of it almost explains itself. Foremost, it has to be sharp and sharp-edged. There's nothing soft about mortar, yet all of your edges in the mortar are soft.

In order to sculpt it, you only need to ask yourself at any point "can this point beneath my pencil see the light? Just partial light? Is it in the shade of an overhanging brick? Or is this a hole that's so deep, the light will not penetrate? If you ask those question as you draw, you'll find yourself drawing three-dimensionally almost without effort.

Incidentally, when I last drew those bricks, I wanted the bricks to look solid and flat, so I made them fairly smooth and removed all traces of white. And I wanted the mortar to look gritty, so I used stippling. I built up the three-dimensional form by placing the dots closer together or further apart. I also stippled in the highlighted areas, and them gently faded the stippling away with Blu-Tack until just a suggestion of them remained. And I used a lightly applied 2H to remove all the white from all areas that weren't highlights. The result was two entirely different surfaces.

I almost forgot to mention that I like your use of strong cast shadows beneath the bricks. They really give depth, and the emphasise the sharp edges of the bricks so they are clearly separated from the mortar.